The present invention pertains to slitting shears comprising two knife shafts, which are adjustable relative to one another and are equipped with at least one knife each.
Machines of this type are used to cut web material. Usual slitting shears contain a frame carrying two columns. The columns carry the mount of two adjustable knife shafts, which can be driven and carry at least one cooperating pair of knives for the cutting operation. One of the columns can be opened for setting and resetting the machine.
The problem arising in the machines is the impairment of the quality of cutting due to wear of the tools. The use of a spring-loaded knife, which shall come reliably into contact with the fixed counterknife because of its elastic properties, has become known for solving this problem. However, the adjustment of the spring-loaded knife has narrow limits, so that the above-mentioned problem will again arise in the case of greater wear on the fixed counterknife.
The basic object of the present invention is to provide shears of the above-mentioned type, with which a constant quality of cut can be guaranteed.
The object is accomplished according to the present invention with the features of claim 1.
Due to knives adjustable in the axial direction of the knife shafts, it is possible to hold the pairs of knives under constant contact pressure with corresponding force-applying means, so that a cutting or separation operation can be achieved with constant quality. The forces are applied for this purpose such that the adjustable knife is placed against the fixed knife of the pair of knives.
The movable knife can be brought into an opened position under the action of a force in the opposite direction, as a result of which the replacement of the tools can be facilitated and expedited.
According to one embodiment of the present invention, a hydraulic or preferably pneumatic force is provided for the movable knife or a knife holder holding the knife. The fluid system may be designed to apply forces in both directions, e.g., by overpressure and vacuum. The hydraulic system makes possible the fine coordination of the force acting on the knife and thus ensures the desired separation or cutting operation. Holes within the knife shaft may be used as guides for a pressurizing medium.
With corresponding selection of the tensioning force, a machine tool is thus created which makes possible the automatic adjustment of the tools, especially knives and spring-loaded knives. Besides the reliable contact of the pair of knives, which is achieved as a result, the machine is made ready for operation in a simpler manner and more rapidly, especially in the case of a tool change.
The use of a mechanical pressurizing means, e.g., a compression spring, for the opening direction of the knife and of a pressurizing medium, e.g., compressed air, as the force in the opposite direction represents a simple solution in terms of manufacturing technology.
The compression spring holds the movable knife holder in an opened position. After an operation and the switching off of the pressure of the medium, the machine can thus be opened immediately for resetting and the adjustment of the knife shaft can be performed without risks after the resetting. The adjustment of the knife or knives is finally carried out automatically by introducing the pressure of the medium.
The embodiment according to the present invention can be used in all slitting shears and independently from the knives used. For example, spring-loaded knives which are arranged on a movable knife holder may be used for the movable knives.
According to another embodiment of the present invention, the knife shafts are equipped with two or more knives, and at least some of the knives and their knife holders are movable.
The knife shafts may be equipped with fixed and/or movable knives as desired. However, a design in which only one shaft is equipped with movable knives is advantageous, especially if a pressurizing medium is used as the pressurizing means.
In one variant, one knife shaft is equipped with fixed knives and knife holders and the other knife shaft with movable knives and knife holders.
According to another embodiment of the present invention, the knife shaft with the movable knives and knife holders also contains fixed knives. The expense is thus reduced without an appreciable impairment in the quality of separation. For example, the fixed knives of this shaft may be placed opposite the less worn fixed knives of the other shaft in this embodiment.
Embodiments in which the knife shaft for the movable knives or a set of tools on the knife shaft is axially displaceable are also conceivable. All knives are thus pressed with equal pressure to the corresponding counterknife, and the differences arising from differences in wear are compensated by the spring-loaded knives.